Laboratory Studies
In patients with medullary sponge kidney (MSK) and hemihypertrophy, serial screening should be performed to exclude malignancies, including abdominal tumors. The following studies are also indicated:
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Urinalysis (ie, assessment of urinary calcium excretion, urine culture)
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A 24-hour urine collection for calcium, magnesium, and citrate: Patients with medullary sponge kidney may have high excretion of lithogenic molecules or low excretion of urinary inhibitors of stone formation.
Imaging Studies
Intravenous pyelography reveals radial, linear striations in the papillae or cystic collections of contrast material in ectatic collecting ducts. The result is a characteristic blushlike pattern to the papillae, the so-called "bouquet of flowers" or "paintbrush" appearance. Typical cases involve all renal papillae but medullary sponge kidney may be unilateral or may affect only a few papillae. Declining use of intravenous pyelography as an imaging technique may result in underdiagnosis of medullary sponge kidney cases.
Renal ultrasonography and CT scanning are unnecessary except to distinguish medullary sponge kidney from papillary necrosis or autosomal dominant polycystic kidney disease.
Intravenous pyelography remains the first-line imaging study for the diagnosis of medullary sponge kidney; however, Pisani et al identified four ultrasonographic findings that can help support the diagnosis, when coupled with clinical findings. [11] These ultrasound findings are as follows:
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Hypoechoic medullary areas
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Hyperechoic spots
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Microcystic dilatation of papillary zone
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Multiple calcifications (linear, small stones or calcified intracystic sediment) in each papilla
The role of MRI is unknown.
Other Tests and Procedures
Other tests
Appropriate workup is needed if medullary sponge kidney appears to be associated with another condition, such as hemihypertrophy or pyloric stenosis, or is part of a syndrome, such as Marfan or Ehlers-Danlos syndrome. This testing should be performed to exclude the presence of a malignancy.
Procedures
No additional, specific diagnostic procedures are warranted for diagnostic evaluation.
Histologic findings
Neither renal biopsy nor nephrectomy is routinely performed.
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Unenhanced coronal volume-rendered (VR) CT image of the kidneys demonstrates 2 small calculi in the mid portion of the right kidney and 2 small calculi in the lower pole of the left kidney (arrowheads). A large low-density lesion in the lower pole of the right kidney and a small low-density lesion in the upper pole of the left kidney (short arrows) were shown to represent benign simple renal cysts on the contrast enhanced CT images. Image courtesy of Dr. Terri J. Vrtiska, Consultant, Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
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CT image of both kidneys demonstrates brushlike densities throughout multiple papillae of both kidneys consistent with renal tubular ectasia. Correlation of the stone disease with the ectatic tubules is diagnostic of medullary sponge kidney. Image courtesy of Dr. Terri J. Vrtiska, Consultant, Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
